Liquid developing agent for electrophotography

ABSTRACT

A liquid developing agent for electrophotography comprising a mixed solution consisting of an insulating carrier liquid containing an organic substance having carboxyl group and a colored solution prepared by solving or dispersing a dye and an amine in a polar solvent which is not miscible with the aforementioned carrier liquid.

United States Patent Inventors l-lazime Machida;

Zenjiro Okuno, both of Tokyo, Japan App]. No. 832,416 Filed June 11,1969 Patented Dec. 7, 1971 Assignee Kabushiki Kaisha Ricoh Tokyo, JapanPriority June 19, 1968 Japan 43/41885 LIQUID DEVELOPING AGENT FOR [56]References Cited UNlTED STATES PATENTS 3,001 ,888 9/1961 Metcalfe et al.252/621 FOREIGN PATENTS 692,023 8/1964 Canada 252/62.1 1,002,061 7/1965Great Britain 252/62.l 1,020,503 5/1966 Great Britain 252/621 PrimaryE.raminerGeorge F. Lesmes Assistant Examiner-J. P. BrammerA!lorney-Woodhams, Blanchard and Flynn ABSTRACT: A liquid developingagent for electrophotography comprising a mixed solution consisting ofan insulating carrier liquid containing an organic substance havingcarboxyl group and a colored solution prepared by solving or dispersinga dye and an amine in a polar solvent which is not miscible with theaforementioned carrier liquid.

LIQUID DEVELOPING AGENT FOR ELECTROPIIOTOGRAPHY BACKGROUND OF THEINVENTION l Field of the Invention The present invention relates to animprovement of liquid developers for electrophotography.

The term electrophotograph" used in the specification is intended tomean a visible reproduction of a so-called electrostatic latent imagesuch as a latent image formed by extinguishing the charge in the exposedarea and preserving the charge in the not exposed area by exposure ofthe photoconductive substances through the original. The copyingmaterial was previously impressed, by corona discharge, with. anelectrical charge all over the photoconductive substance.

2. Description of the Prior Art As the developing solution for wetprocess electrophotography which is used for developing the latentelectrostatic image, there is used a solution prepared by dispersingcoloring particles such as carbon black .in a carrier liquid of highresistance and low dielectric constant together with apolaritycontrolling agent like a resin, if necessary. Thepolarity-controlling agent behaves in such a way as to give the coloringparticles the polarity necessary for them to stick fast to theelectrostatic latent image and to act as a dispersing agent forachieving the colloidal stability of the liquid developer, and saidagent also has a property of fixing the copied image after thedevelopment has been completed. Organic hydrocarbon solvents aregenerally used as a carrier liquid of the liquid developer of this typebut they have a defect of being inflammable. There are other types ofwidely known carrier liquids, one of which comprises a halogenatedhydrocarbon and the other of which comprises fluorinated hydrocarbons,both being free from inflammability; however, they have their respectivedefects, the former being not satisfactory because of its toxicity andthe latter because of its high price.

In another case where an electrostatic latent image is developed by thedirect use of water as a carrier liquid, the development procedure israther difficult because the electrostatic latent image is marredheavily. For instance, a liquid developer of W/O emulsion type preparedby adding water, equal in quantity to the undermentioned carrier liquid,to a liquid developer obtained by dispersing a polarity-controllingagent and coloring particles in a carrier liquid of high resistance hasbeen widely known. This liquid developer only aims at eliminatinginflammability of the liquid developer by emulsifying water therein bythe use of an emulsifying agent, which results in the presence ofunnecessary minute water beads which make no contribution to thedevelopment of the electrostatic latent image, in the liquid developerwherein a solution of high resistance and low dielectric constant isused as a carrier liquid. Liquid developers of this type have nosatisfactory emulsion stability and since they are substantiallyprepared according to a method in which the coloring particles whichhave absorbed not so much controlling agent are depositedelectrostatically on the latent image, the resultant image does not havevery good fixedness.

SUMMARY OF THE INVENTION The present invention relates to a liquiddeveloping agent for electrophotography comprising a mixed solutionconsisting of a carrier liquid containing an organic substance having acarboxyl group and a colored solution prepared by solving or dispersinga dye and an amine in a polar solvent which is not miscible with theaforementioned carrier liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As specific examples of a polarsolvent immiscible with a carrier liquid that can be used in thisinvention there are enumerated water, alcohols, acetone, methylcellosolve, dimethyl-formamide and dioxane. For the dyes, in addition todyes which are either soluble or insoluble in the aforementioned polarsolvent and are insoluble in the carrier liquid, for

.instance, alkali blue (0]. Acid Blue 119), carbolan crimson (C.l. AcidRed 138), carbolan blue (C.l. Acid Blue 138) and the like, such dyes asaniline black (CI. Pigment Black 1), spirit black (C.I. Solvent Black 5)and the like having an amino group which coordinates with carboxylicacid can be used effectively. As the amine to be used, it should be anamine of such type as to coordinate with carboxylic acid, namely atertiary amine to be converted to a quaternary salt compound bycoordinating with a carboxyl group. The amine is required to be solublein the aforementioned polar solvent and immiscible with the carrierliquid. Trimethylamine, triethylamine and triethanolamine, for instance,may be mentioned as being suitable.

As for the organic substance having a carboxyl group and which is to bedissolved in the carrier liquid, besides acrylic acid, polymers andcopolymers such as acrylates or methacrylates which contain methacrylicacid, and such unsaturated resins as alkyd resin, maleic acid resin andthe like, varnish, rosin and such higher fatty acids as stearic acid andoleic acid can be used. Referring to the carrier liquid, in addition tosuch hydrocarbon halogenide as toluene, carbon tetrachloride, any of thechemicals, such as naphtha, isoparaffin and paraffin, that have hithertobeen commonly used as a carrier liquid of liquid developers can be usedin practising this invention.

The procedure to make the liquid developing agent according to thepresent invention consists of preparing a colored solution obtained bysolving or dispersing the aforementioned dyes and amine in a polarsolvent and a solution obtained by solving an organic substance whichhas a carboxyl group in a carrier liquid. Both of the solutions aremixed and stirred fully with a mixer like a homogenizer until adeveloper of a perfectly homogenized emulsion or suspension is obtained.When dyes having an amino group which coordinate with the carboxylicacid are used in making the developer, the quantity of amine to be addedcan be decreased to such a degree as to make the amine existing in thecolored solution in sufficient quantity to enable it coordinate with thecarboxyl group of the organic substance dissolved in the carrier liquid.The emulsification can be promoted by making the colored solution afatty acid ammonium salt with by the addition of fatty acid beforehandor by using a proper surface active agent if the emulsification orsuspension is found to be imperfect.

As mentioned in the foregoing, the developing agent according to thepresent invention is an emulsion or suspension of a colored polarsolution which contains an amine and a solution of a high resistance andlow dielectric constant which contains carboxyl group. It is importantto determine the ratio of the ingredients of the developing agent insuch a way as to present a distinct polarity when the electrostaticlatent image is developed. To achieve this purpose it is necessary tomix more than one part by weight of the carrier liquid with one part byweight of the colored solution. A developing agent wherein water isspecifically used as a polar solvent to solve the dye is perfectly freefrom inflammability. Furthermore, the developing agent preparedaccording to the present invention possesses many excellent merits suchas greatly improved dispersibility and stability when compared withthose conventional developing agents which are prepared by simplydispersing the polar solvent, in which dyes are solved, in the carrierliquid, since the carboxyl-containing organic substance in the carrierliquid coordinates with the amine contained in the colored solution inwhich dyes are solved to display an excellent surface activity, and thefixing property of the image is improved very much due to the highlypolymerized substance abundantly contained in the developing agent.

EXAMPLE 1 A paste was prepared by mixing a solution, which had beenobtained by solving 1 g. of water-soluble carbolan crimson(anthraquinone acid dye manufactured by l.C.1.) in g. of 1 percenttrimethylamine-naphthenic acid aqueous solution, 3 percent (by weight)acrylate copolymer and l00 g. of

toluene in the homogenizer for minutes. Ten parts of this paste wasdispersed in 50 parts of lsopar H (petroleum hydrocarbon manufactured byEsso Standard Oil Company) to obtain the developing agent. Thedeveloping performance of the developing agent thus prepared was notinterfered so far as the content of dispersed A paste did not exceed 30parts.

EXAMPLE 2 B solution was prepared by mixing a solution obtained bysolving 125 g. of water soluble carbolan green (anthraquinone acid dyemanufactured by l.C.l.) in 150 g. of 1 percent triethanolamine-oleicacid aqueous solution, 3 percent copolymer of styrene methacrylic acidbutyl acrylate (mole ratio 50:30:20) and toluene in the homogenizer forminutes. Ten parts of this B solution was dispersed in 50 parts ofnaphtha No. 6 to obtain the developing agent. The developing property.of the developer thus obtained was not destroyed when the quantity of Bsolution dispersed in the developer was not in excess of 30 parts.

EXAMPLE 3 One g. of spirit black was mixed with 100 g. of 1 percenttriethyl-amine-stearic acid aqueous solution with the homogenizer. Thismixture 5 percent copolymer of ethyl acrylate-vinyl benzoic acid-laurylmethacrylate and 50 g. of toluene were mixed with the homogenizer toobtain C solution. Ten parts of this C solution was dispersed in 50parts of lsopar H to prepare the developing agent. N0 damage of thedeveloping property was observed so far as the quantity of the dispersedC solution remained within the region of 30 parts.

EXAMPLE 4 One g. of aniline black was solved in 100 g. of 1 percenttrimethylamine-naphthenic acid. Twenty parts of this solution wasdispersed in 50 parts of naphtha No. 6 'to obtain the developing agent.

When the respective developing agents prepared according to theaforementioned examples 1-4 were used to develop the electrostaticlatent image of electrophotographic photoconductive paper, each of themproduced a clear image and all of the developing agents were found to bestable enough not to show any sign of deteriorated dispersion.

What we claim is:

1. In a liquid developer for electrophotography comprising a carrierliquid selected from the group consisting of toluene, carbontetrachloride, naphtha and isoparaffic and paraffinic hydrocarbons, saidcarrier liquid having emulsified or suspended therein a colored solutionor dispersion of a dye and a polar solvent, saiddye being selected fromthe group consisting of alkali blue (C.l. Acid Blue 119), carbolancrimson (C.I. Acid Red 138), carbolan blue (C.l. Acid Blue 138), anilineblack (CI. Pigment Black 1), and spirit black (C.l. Solvent Black 5 saidpolar solvent being selected from the group consisting of water,acetone, methyl cellosolve, dimethylformamide and dioxane, theimprovement in which said colored solution or dispersion containsdissolved therein a tertiary amine selected from the group consisting oftrimethylamine, triethylamine and triethanolamine, and said carrierliquid contains dissolved therein a carboxyl-containing organic materialselected from the group consisting of acrylic acid, acrylate copolymercontaining methacrylic acid, methacrylate copolymer containingmethacrylic acid, alkyd resin, maleic acid resin, varnish, rosin,stearic acid, oleic acid, styrenem ethacrylic acid-butyl acrylatecopolymer and ethyl acrylatevinyl benzoic acid-lauryl methacrylatecopolymer, the weight of said carrier liquid present in said developerliquid being greater than the weight of the colored solution ordispersion present'in said carrier liquid.

2. A liquid developer according to claim 1 wherein said colored solutionis emulsified in said carrier liquid.

37 A liquid developer according to claim 1 wherein said coloreddispersion is suspended in said carrier liquid.

4. A liquid developer according to claim 1 wherein said polar solvent iswater.

5. A liquid developer according to claim 2 wherein said dye is dissolvedin the polar solvent.

6. A liquid developer according to claim 3 wherein said dye is dispersedin the polar solvent.

2. A liquid developer according to claim 1 wherein said colored solutionis emulsified in said carrier liquid.
 3. A liquid developer according toclaim 1 wherein said colored dispersion is suspended in said carrierliquid.
 4. A liquid developer according to claim 1 wherein said polarsolvent is water.
 5. A liquid developer according to claim 2 whereinsaid dye is dissolved in the polar solvent.
 6. A liquid developeraccording to claim 3 wherein said dye is dispersed in the polar solvent.